Flexible wires which can be guided by torquing into small-vessel sites in the body, such as along vascular pathways or ducts, have a number of uses in medicine. One important use is as a catheter guide wire. In this application, the wire typically is fed through the catheter lumen and the catheter and wire are guided as a unit, by wire torquing, toward the target site. If the target site is deep within a soft-tissue, and can be accessed only along a tortuous,,.small-vessel path, it is usually necessary to alternately advance the more flexible guide wire ahead of the catheter, then thread the catheter along the advanced portion of the wire. By first preshaping (curving) the guide wire tip, and by torquing the guide wire during catheter placement, the wire can be directed into side-branching vessels and the catheter can then be advanced over the wire into the branching vessel. When the target site is reached, the wire can be withdrawn to allow fluid material to be injected through the catheter.
The wire may also be used as a radio-opaque probe for use in localizing sites of pathology, such as tumor regions, within the body. Here the wire, equipped with a radio-opaque probe, is guided to the site of interest by radiographic imaging. Once the probe is in place, its location can be used for guiding the delivery of drugs into or focusing radiation at the site, or as a site marker for surgical excision. The probe may also be used as a microwave antenna, for producing localized heating at the probe site in response to microwaves directed at the probe. A wire of this type may also be used for dislodging or puncturing plaque deposit material in a vessel, or for purposes of making the vessel accessible to catheter entry and/or balloon placement in the region of plaque.
Torqueable wires which can be guided into small-vessel sites, along tortuous vessel paths, have been proposed heretofore. Typically, these wires are formed of flexible, torqueable filament material, such as stainless steel, and have preferred diameters between about 8-40 mils (thousandths of an inch). The wire may be provided with a bent distal tip, or a bent spring coil tip which can be oriented, by torquing the opposite end of the wire, to follow a desired pathway at a vessel branching. Ideally, torque transmission should be controlled, such that a selected amount of torquing produces a desired amount of wire rotation at the bent distal tip.
In order to achieve both good torqueability along the wire and good flexibility at the distal end region of the wire, for movement through tortuous, small-vessel pathways, guide wires having relatively large-diameter body portions and tapered distal end regions have been proposed, such as in U.S. Pat. No. 4,545,390. Typically in this type of wire, the body portion is up to 200 cm or more in length, and the tapered region, 5-50 cm or longer. The relatively large diameter of the body portion wire, e.g., 14-40 mils, reduces the possibility of wire twisting, shearing and/or deformation in response to a torque applied to the wire. At the same the relatively greater flexibility in the tapered segment facilitates wire movement through sharp-bend regions in small-vessel pathways.
The wire construction just described preferably includes a coil spring which encases a major portion of the tapered end region, typically terminating at the end of the wire. In this construction, the core wire serves to transmit torque to the guide wire tip for wire steering into side-branching vessels, to transmit axial forces, and to support the catheter. The coil functions to provide column strength to the guide wire tip, and to increase the surface area of the tip region, to reduce the stress of the wire tip in contact with a vessel wall. Where the coil is formed of platinum or gold or tungsten, the coil also serves to enhance the radio-opacity of the wire tip. The coil also presents a soft end to prevent vessel trauma. The coil is typically attached as by brazing or soldering to the wire at the wire's distal tip and at the proximal end of the coil. It can be appreciated that the point of attachment of the spring coil to the wire, at the coil's proximal end, creates a step in the axial profile of the tapered wire region. Potentially this step creates a source of roughness which can injure vessel lining, and also become caught at the distal opening of the catheter, as the guide wire is withdrawn from the catheter. The latter may cause the coil to be pulled off the wire, particularly since the attachment of the coil to the wire at the step tends to be weak for lack of common bonding area between the coil and wire. The difference in coil and wire diameter at the coil end can be reduced by forming a reduced-diameter step in the wire, to accommodate the added thickness of the coil. However, the step in the wire creates a zone of poor torque transmission, and also allows sharp wire bending to occur.